Updated 12 October 2026 · By Pete Bromfield, former Head of Maths with IB examining experience

Has my pocket money kept up with inflation?

AI SLAA SLAI HL Accessible Also in: Statistics

Research question

What is the real value of my pocket money (or a part-time wage) over the last ten years, and would indexing it to a student-relevant basket of prices give a different answer from the official inflation index?

Make it yours, then agree it with your teacher.

Next step: plan this IA free — the planner opens with this question filled in. For feedback on your own draft, the IA package (€39 once) gives you 5 AI feedback credits and every annotated exemplar in full.

Why it makes a good exploration

Inflation is abstract until it shrinks your own money. Building your own price index for things students buy — and comparing it with the official one — makes this very personal.

The mathematics you'll need

Percentage change and compound growth
Price indices and weighted means
Real vs nominal values
Exponential models of prices

Modelling the data, step by step

This idea usually needs an exponential model. See it worked step by step, with a criterion tip at every step: Exponential y = a e^(kx) + c and y = a·bˣ.

Model your own data Paste it from Desmos, GeoGebra or a spreadsheet and get the same play-by-play with your numbers. New to modelling? Start with the modelling workflow. Writing it up? The IA modelling planner comments on each paragraph as you draft — it never writes it for you.

Where the data comes from

Official consumer price index series; prices of items you buy from receipts, archived menus or published average prices.

Office for National Statistics (UK) — UK population, earnings, inflation, births and deaths time series.
Eurostat — EU statistics by country and region (prices, energy, transport, education).
FRED (Federal Reserve Bank of St. Louis) — 800,000+ economic time series (interest rates, inflation, unemployment) with CSV download.

Real data for this idea

Primary source: Office for National Statistics (UK): CPIH annual rate (series L55O). Download the CSV of monthly and yearly 12-month rates. Licence: Open Government Licence v3.0: free to reuse with an acknowledgement.
Also useful: Office for National Statistics (UK): CPI index (series D7BT). The index (2015 = 100) by month, to turn past amounts into today's prices.

If you use FRED (listed above), treat it as link-only: download series for your own analysis, but link to them rather than copying FRED's data into anything you publish. Links checked October 2026; we link to the data and never copy it. More free data sets.

A possible outline

Explain how an official price index is built.
Compute the real value of your money over time.
Build a student basket with justified weights.
Compare the two indices.
Reflect on substitution and quality changes.

Pitfalls that cost marks

Weights with no justification.
Comparing prices from different shops or sizes.
Confusing percentage points with percentages.

Showing personal engagement

Use your own spending records.
Survey classmates to set basket weights.
Negotiate a pocket-money rise using your model (and report the result).

See Criterion C: personal engagement for what examiners look for.

Which course is it for?

Course	Fit	Maths to lean on
AA SL	Good fit	Percentage change and compound growth; Price indices and weighted means
AA HL	Not a natural fit	The mathematics is mainly from the AI course; at AA HL the exploration would need an AA-level approach (calculus, proof or probability theory) to reach the top of Criterion E.
AI SL	Good fit	Percentage change and compound growth; Price indices and weighted means
AI HL	Fits, but add an HL technique	Percentage change and compound growth; Price indices and weighted means

Level: Accessible. A good first extended piece of maths, with room to go deeper. See how the IA differs between AA and AI, SL and HL.

How this idea reaches the top bands

Reflection (D)

For this idea, start with the weak points: weights with no justification; and comparing prices from different shops or sizes. Say how each one affects your answer.

Use of mathematics (E)

SL: percentage change and compound growth; price indices and weighted means; real vs nominal values; exponential models of prices, each explained in your own words and carried out correctly.

How finance explorations reach the top bands in general: Finance & economics IA ideas. Guides: A · B · C · D · E · self-grade sheet.

Taking it further

Fit exponential models to each item's price and compare their growth rates.

Extending it for HL

Add an HL technique the question genuinely needs: what an HL finance exploration adds.

See a complete IA, marked

Should I lease or buy my first car? (AI SL) is a complete finance exploration, marked on every criterion.

Frequently asked questions

Which IB Maths course is this IA idea for?

It works for AI SL, AA SL and AI HL. We rate it Accessible: a good first extended piece of maths, with room to go deeper.

What mathematics does this IA use?

Percentage change and compound growth, price indices and weighted means, real vs nominal values and exponential models of prices.

Where can I get data for this IA?

Official consumer price index series; prices of items you buy from receipts, archived menus or published average prices. Checked sources and tools: Office for National Statistics (UK), Eurostat and FRED (Federal Reserve Bank of St. Louis).

Turn this idea into your IA

The planner opens with “Has my pocket money kept up with inflation?” filled in: the question, the maths and the data sources.

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